1. Field of the Invention
The present invention relates to a method of forming a via hole through a glass wafer. More particularly, the present invention relates to a method of forming a via hole through a glass wafer without producing an undercut.
2. Description of the Related Art
It is generally known in the art that a via hole (or simply a “via”) necessarily should be formed in a wafer level of a micro-electromechanical system (MEMS) packaging utilizing glass to permit the electrical processing of elements in the MEMS. In a conventional method of forming a via hole in a wafer level, however, since the via hole is formed by sandblasting after being patterned on a surface of the glass wafer, it is problematic in that the formed via hole may have an undercut portion and a rough surface. This undercut problem is especially pronounced in the formation of a via hole having a small diameter. In this case, not only is it difficult to etch the via hole, but the formed via hole may also have an undercut portion that causes a severe problem.
FIG. 1 illustrates a sectional view of a via hole formed through a glass wafer 100 using a conventional process, in which the via hole has an undercut portion 10 formed at a lower end thereof and a rough surface 20. FIGS. 2A and 2B are photographs showing enlarged views of a via hole, which is formed in an actual glass wafer using a conventional process, and an undercut portion formed at a lower end of the via hole, respectively.
In order to reduce formation of the undercut portion at the lower end of a via hole as described above, conventional methods of forming a via hole have employed a chemical mechanical polishing (CMP) step or a thick deposition of a metal film that enables electrical connection. In the case of the method employing the CMP step, however, since a portion of the glass surface is completely eliminated, characteristics of elements may be damaged in a packaging in which the delicate glass surface plays an important role. Further, the method employing the deposition of a metal film requires increased manufacturing steps and manufacturing cost.
Moreover, when the via hole is formed by sandblasting, the via hole may not only have a rough surface, but may also have minute cracks formed therein.